The invention relates generally to fluid level sensors, such as acoustic transducers that emit and receive acoustic pulses. More particularly, the invention relates to techniques for mounting ultrasonic fluid level sensors in a container in an intrusive arrangement so that the fluid in the container wets the transducer active surface.
The use of acoustic transducers for determining fluid levels in containers is well known. In one form of use known as intrusive, an acoustic transducer is mounted within the container so that the transducer emits the acoustic pulses directly into the fluid. Typically, a stillwell is used to reduce the effects of bubbles in the fluid, or fluid swashing around the transducer, as well as to provide a channel for the acoustic waves to follow to the surface of the fluid.
A typical application of an intrusive transducer is with fuel tanks used on aircraft. By mounting a transducer at the bottom of a tank, the transducer can be used to emit pulses towards the fuel surface. The round trip time for the acoustic energy to be reflected back to the transducer can be correlated with the fuel height when the velocity of the acoustic pulses in the fuel is known.
Numerous problems are encountered with the known fuel sensor mounting arrangements. Among them is the fact that sensors typically are mounted to the tank in such a manner that in order to remove a sensor (such as for repair or replacement during routine maintenance) the fuel must first be removed from the tank. Draining the fuel for simple replacement of a sensor is an expensive and time consuming task. In other mounting arrangements, the sensors are fixed to the tank wall, thus not only requiring draining the fuel but also an extensive tear down of the fuel tank.
The latest generation aircraft are expected to make extensive use of composite materials for the wings. In circumstances where the wing also serves as the fuel tank, tear down for sensor replacement will not be acceptable maintenance practice.
The need exists, therefore, for an intrusive sensor mounting arrangement that permits quick and easy sensor installation and removal without needing to drain the fuel prior to sensor removal. The mounting arrangement should also provide minimal fuel displacement from the fuel tank when a sensor is removed; and the sensor should be installable and removable without tank or structural tear down or damage.